[BC] Harris SX-1 Spur Problem

[Dan Dickey]

You don't say whether this transmitter has a synthesizer or a crystal 
oscillator.  If a synthesizer is in it I would look at the RF output to see 
if the spurs are there or not.  Even if it has a crystal oscillator I would 
still look at the RF output on an SA to see if the spurs are there or not.

Someone else pointed out dried capacitors that might let a linear regulator 
oscillate.  The most likely suspect after the oscillator card would be the 
PDM generator.  If you have an SA that goes down to audo frequencies look at 
one of the PDM outputs on that card for a noise signal at 50kHz with no 
modulation but the transmitter running at normal power.  You should see 
60kHz but not 50kHz.  If the noise is there then you have it pinned down to 
that card or it's power supply.

There are some of us old guys who still know that transmitter.  Let us know 
if you find anything or need some more suggestions.

Best regards,
Dan Dickey



----- Original Message ----- 
From: "James Boyd" <bbts at easystreet.com>
To: <broadcast at radiolists.net>
Sent: Sunday, November 27, 2005 9:48 AM
Subject: [BC] Harris SX-1 Spur Problem


>I have a Harris SX-1 in my care that has a spur problem.  Modulated spurs 
>at
> plus and minus 50 kHz from the carrier at about 45 dB down from carrier.
> The usual suspects have been checked.  PDM frequency is on at 60 kHz.  PDM
> waveform is fine.  Output of oscillator is spectrally ok.  All mosfets in
> PDM and PA are ok.  All power supply voltages are in spec.  Have looked at
> power supplies with scope to see if any regulators are oscillating. 
> Nothing
> found.  All of the big caps have been replaced.  Anyone have any ideas of
> the cause of such a problem?
>
> James Boyd
> Boyd Broadcast Technical Services
> Tualatin, OR
>
>
> _______________________________________________
> This is the BROADCAST mailing list
> To send to the list, email: broadcast at radiolists.net
> For sub changes, archives and info on this other lists: 
> http://www.radiolists.net/